Working vehicles often include auxiliary hydraulic systems configured to supply pressurized hydraulic fluid from a vehicle hydraulic pump to auxiliary equipment or attachments. For example, agricultural and construction equipment vehicles (e.g., tractors; tractor-loaders; skid-steer loaders) may be coupled to attachments such as augers, grapples, sweepers, landscape rakes, backhoes, scarfers, snowblowers, stabilizers, raising and lowering implements or other attachments driven by hydraulic actuators such as hydraulic cylinders or hydraulic motors.
The attachments can be referred to as "auxiliary" equipment since they are typically connected to a vehicle to perform a particular job, and then disconnected when the job is complete. Accordingly, the working vehicles include external fluid fittings to faciliate connecting and disconnecting the hydraulic fluid supply lines of the attachments to the vehicles' auxiliary hydraulic systems. The auxiliary hydraulic systems include valves configured to control the supply of hydraulic fluid flowing through the fittings. The use of auxiliary equipment increases versatility of working vehicles by allowing the vehicles to perform different functions at different times.
Different attachments impose varying requirements on auxiliary hydraulic systems with respect to timing, rate and control of fluid flow. For example, an attachment equipped with a hydraulic motor (e.g., auger) may require a continuous flow of fluid while an attachment equipped with a hydraulic cylinder actuator (e.g., plow) may only require a flow of fluid for a discrete period. A desired rate of flow may depend upon the weight of an implement or on the work being performed by an attachment. For example, the flow rate required to raise an implement at a desired speed (e.g., fast enough for efficiency yet slow enough for safety) may be higher for a relatively heavy implement than for a relatively light implement. Closed-loop control based upon feedback signals may or may not be required. For example, a plow can be raised and lowered between desired raise and lower positions by a hydraulic cylinder actuator based on position feedback signals while a landscape rake may be raised or lowered by applying a fluid flow for a period sufficient to fully raise or lower the rake. Further, an auxiliary hydraulic system may be required to supply fluid to an attachment at a maximum flow rate in some situations and at a "feathered" flow rate (e.g., proportional control) in other situations such as during precision operations.
An auxiliary hydraulic system may also be required to provide hydraulic fluid flows to a number of auxiliary attachments having different fluid flow timing, rate and control requirements. For example, a tractor could be required to provide hydraulic fluid to simultaneously raise and lower a plow based upon position feedback signals, raise and lower a rake, and drive an auger.
Accordingly, it would be advantageous to provide an improved auxiliary hydraulic system capable of providing pressurized fluid to attachments in continuous or timed modes, of providing fluid to attachments at flow rates which can be set by an operator, of providing fluid to certain attachments using closed-loop control based upon feedback signals, and of providing fluid to attachments at maximum or feathered flow rates. Further, it would be advantageous to provide an improved auxiliary hydraulic system for supplying pressurized fluid to attachments having varying timing, rate and control requirements.
It would also be advantageous to provide an improved method of reading the position of a command device in an auxiliary hydraulic control system or any other type of control system. Advantages which can be realized by the improved method disclosed herein include accurately reading an operating position of a command device (e.g., a control lever) which can be moved between predefined positions (e.g., detents). The method can generate a calibrated command signal representing a predetermined command value such as a neutral command value or a command limit when the command device is moved into a corresponding predefined position. The method can further generate a calibrated command signal representing a proportional command value when the command device is between the predefined positions. The method can also generate an accurate position signal without the need for a high-accuracy potentiometer coupled to the command device. Further, the method can determine when a control system is configured with a particular command device.